About NGC 3314

By Bill Keel (University of Alabama, Tuscaloosa)

NGC 3314 lies in Hydra (to be precise, at equinox
2000 coordinates 10 37 12.8 -27 41 04), and at least
one of the galaxies is a member of the Hydra I cluster
of galaxies (also known as Abell 1060). Its existence
is no great secret, since this part of the sky was
depicted in the cover shot of every CDROM box for
the southern Digitized Sky Survey, and its nature
is noted in the caption for the
Abell 1060 photograph distributed by the Royal
Observatory Edinburgh (look under "Galaxy Clusters"
- the picture referred to is available below).
However, long-exposure photographs saturated the
inner parts, making this look like a galaxy blowing
off material in the manner of M82
and so hiding its real nature. I first learned of
it from seeing some photographs taken with the 1.5-meter
telescope at Cerro
Tololo by Dan Weedman and Malcolm Smith, with
a range of exposure times so that the dark spiral
dust lanes stood out in some pictures.

The
two galaxies involved have been designated as NGC
3314a (the foreground spiral) and NGC 3314b (the
more inclined background object). Their redshifts
are quite different - 2851 km/s for NGC 3314a and
4641 km/s for NGC 3314b. The mean value for the
cluster Abell 1060 is about 3400 km/s (corresponding
to a distance of about 42 megaparsecs = 140 million
light-years), with a dispersion for clear members
of about +/-600 km/s. Thus the velocities of both
galaxies are consistent with being cluster members
in the outer envelope of its velocity range. However,
maps in the 21-cm emission of neutral hydrogen by
Pauline McMahon and colleagues using the Very Large
Array show that NGC 3314a is one of several spiral
galaxies at very similar redshift and almost connected
by tenuous streamers of gas, suggesting that these
galaxies form a distinct group in front of Abell
1060. Either way, we are
pleased that there's no direct evidence of interaction
between NGC 3314a and b which would complicate our
ability to interpret measurements of the dust in
NGC 3314a.

How far away are the two
galaxies, from us and from each other?
I won't pretend to know the distance to Hydra I
to better than 10 Mpc. More to the point, let's
be good HST types and call the Hubble constant 80
km/s/Mpc. The best evidence puts NGC 3314 in a group
at mean redshift 2810 km/s, for a redshift distance
of distance 35 Mpc. Abell 1060 has mean redshift
3418 km/s for a distance of 43 Mpc. Not that I'd
put too much faith in the exact numbers, but unless
we're being fooled by the dynamics, the two galaxies
are 5-8 Mpc apart. So in light-years,
I'd call that 115 and 140 million from us, and something
like 25 million apart.

How big is NGC 3314?
Current catalog entries aren't too helpful because
they deal with the blended light of the two galaxies
in odd ways. From the HST data, the bright part
of the combined image subtends an area 1.0 by 1.7
arcminutes which projects to 12 by 21 kiloparsecs
at the distance of Abell 1060. By
themselves, NGC 3314a would be about 1.3 by 1.3
minutes and NGC 3314b about 0.7 by 1.7.

How bright?
Similarly, existing catalogs give rough magnitudes
for the two components, which depend strongly on
how you take the image apart (and what you assume
about the effects of dust). Again
from the HST data, we derive a total magnitude for
the part shown in the Heritage image of 13.5 in
blue light, or about 12.8 in the visual band.

In
a large amateur telescope, this is a very interesting
region. The cluster center lies only 12 minutes
of arc away, between the giant elliptical galaxies
NGC 3309 and 3311, and just to their east is the
giant spiral NGC 3312 (probably a cohort of NGC
3314a, along with the small ringlike galaxy to the
east of NGC 3312). The cluster includes a total
of ten galaxies bright enough to be listed in the
NGC catalog, within 1/2 degree of its center. You
can see some of these in this 0.35-degree
portion of the Southern Sky Survey, extracted
by Skyview
(noting the
copyright data for these images). NGC 3314 is
at lower left, on the southeastern fringes of the
cluster region. NGC 3314 appears just to the southeast
of a brighter star (magnitude 12), which is superimposed
on the outer fringe of NGC 3314b. We took special
care to keep this star out of the field of the CCD
(and on another CCD of WFPC2) in planning the HST
observations, to avoid problems with scattered light
overwhelming part of the galaxies.